cool viewport

editor/main.cpp

@@ -21,16 +21,15 @@ class Editor : public sophia::Application {
 
     sophia::SceneHandle sceneHandle = scenes().create();
     sophia::Scene& scene = scenes().get(sceneHandle);
-    sophia::Entity camera = createDemoScene(scene);
+    createDemoScene(scene);
 
     panels().emplace<SceneHierarchyPanel>(scene, selected);
     panels().emplace<InspectorPanel>(selected, textures);
     panels().emplace<AssetBrowserPanel>();
     sophia::RenderTargetHandle sceneTarget =
         resources().create<sophia::RenderTarget>();
-    views().create(
-        {.scene = sceneHandle, .target = sceneTarget, .camera = camera});
-    panels().emplace<ViewportPanel>(ui(), sceneTarget);
+    views().create({.scene = sceneHandle, .target = sceneTarget});
+    panels().emplace<ViewportPanel>(ui(), sceneTarget, scene, selected);
 
     panels().setDefaultLayout(
         {.left = {"Scene Hierarchy"},
@@ -42,10 +41,8 @@ class Editor : public sophia::Application {
   void onUpdate(const sophia::FrameInfo& frameInfo) override {}
 
  private:
-  sophia::Entity createDemoScene(sophia::Scene& scene) {
-    sophia::Entity camera = scene.createEntity("Main Camera");
-    camera.addComponent<sophia::CameraComponent>();
-    scene.setActiveCamera(camera);
+  void createDemoScene(sophia::Scene& scene) {
+    scene.createCamera("Main Camera");
 
     sophia::Entity checker = scene.createEntity("Checker");
     checker.getComponent<sophia::TransformComponent>().position = {-1.5f, 0.f,
@@ -66,8 +63,6 @@ class Editor : public sophia::Application {
         sophia::SpriteComponent{.color = {0.25f, 0.45f, 0.95f, 0.6f},
                                 .size = {2.f, 2.f},
                                 .sortOrder = 1});
-
-    return camera;
   }
 
   sophia::TextureHandle createCheckerTexture() {

editor/panels/viewport_panel.cpp

@@ -2,7 +2,86 @@
 
 #include <imgui.h>
 
+#include <array>
+#include <optional>
+#include <sophia/components.hpp>
+#include <tuple>
+
+namespace {
+
+// Corners of the unit quad a SpriteComponent's model matrix maps to world.
+constexpr std::array<glm::vec2, 4> UNIT_QUAD{
+    glm::vec2{0.f, 0.f}, glm::vec2{1.f, 0.f}, glm::vec2{1.f, 1.f},
+    glm::vec2{0.f, 1.f}};
+
+const ImU32 SELECTION_COLOR = IM_COL32(255, 170, 40, 255);
+
+}  // namespace
+
+ImVec2 ViewportPanel::ViewportTransform::worldToScreen(
+    const glm::vec3& world) const {
+  glm::vec4 clip = viewProjection * glm::vec4{world, 1.f};
+  glm::vec2 ndc = glm::vec2{clip} / clip.w;
+  // Vulkan NDC has +y pointing down, same as the screen.
+  return {origin.x + (ndc.x * 0.5f + 0.5f) * size.x,
+          origin.y + (ndc.y * 0.5f + 0.5f) * size.y};
+}
+
+glm::vec2 ViewportPanel::ViewportTransform::screenToWorld(
+    const ImVec2& screen) const {
+  glm::vec2 ndc{(screen.x - origin.x) / size.x * 2.f - 1.f,
+                (screen.y - origin.y) / size.y * 2.f - 1.f};
+  glm::vec4 world = inverseViewProjection * glm::vec4{ndc, 0.f, 1.f};
+  return glm::vec2{world} / world.w;
+}
+
 void ViewportPanel::onUpdate(const sophia::FrameInfo&) {
+  drawToolbar();
+  ImGui::Separator();
+
+  const ImVec2 origin = ImGui::GetCursorScreenPos();
+  const ImVec2 size = ImGui::GetContentRegionAvail();
+  if (size.x < 1.0f || size.y < 1.0f) {
+    return;
+  }
+
+  ui.image(target);
+
+  // The image doesn't take mouse input, so without this, dragging in it
+  // would drag the window instead.
+  ImGui::SetCursorScreenPos(origin);
+  ImGui::InvisibleButton("##viewport", size);
+
+  ImDrawList* drawList = ImGui::GetWindowDrawList();
+  drawList->PushClipRect(origin, ImVec2(origin.x + size.x, origin.y + size.y),
+                         true);
+
+  if (showGrid) {
+    drawGrid(origin, size);
+  }
+
+  sophia::Entity camera = scene.getActiveCamera();
+  if (camera && camera.hasComponent<sophia::CameraComponent>()) {
+    // Use the panel's size rather than the target's: the target is resized
+    // a frame late, and the mouse is over the panel.
+    float aspect = size.x / size.y;
+    glm::mat4 viewProjection =
+        camera.getComponent<sophia::CameraComponent>().getViewProjection(
+            camera.getComponent<sophia::TransformComponent>(), aspect);
+
+    ViewportTransform viewport{origin, size, viewProjection,
+                               glm::inverse(viewProjection)};
+    handleInput(viewport);
+    drawSelection(viewport);
+  }
+
+  drawList->PopClipRect();
+
+  ImGui::SetCursorScreenPos(ImVec2(origin.x + 8.0f, origin.y + 8.0f));
+  ImGui::TextDisabled("%.0f x %.0f", size.x, size.y);
+}
+
+void ViewportPanel::drawToolbar() {
   const struct {
     const char* label;
     GizmoMode mode;
@@ -17,20 +96,14 @@ void ViewportPanel::onUpdate(const sophia::FrameInfo&) {
     ImGui::SameLine();
   }
   ImGui::Checkbox("Grid", &showGrid);
+}
 
-  ImGui::Separator();
-
-  const ImVec2 origin = ImGui::GetCursorScreenPos();
-  const ImVec2 size = ImGui::GetContentRegionAvail();
-  const ImVec2 end(origin.x + size.x, origin.y + size.y);
-
-  ui.image(target);
-
-  ImDrawList* drawList = ImGui::GetWindowDrawList();
-
-  if (showGrid) {
+void ViewportPanel::drawGrid(ImVec2 origin, ImVec2 size) {
   constexpr float GRID_STEP = 40.0f;
   const ImU32 gridColor = IM_COL32(255, 255, 255, 18);
+  const ImVec2 end(origin.x + size.x, origin.y + size.y);
+
+  ImDrawList* drawList = ImGui::GetWindowDrawList();
   for (float x = GRID_STEP; x < size.x; x += GRID_STEP) {
     drawList->AddLine(ImVec2(origin.x + x, origin.y),
                       ImVec2(origin.x + x, end.y), gridColor);
@@ -39,8 +112,91 @@ void ViewportPanel::onUpdate(const sophia::FrameInfo&) {
     drawList->AddLine(ImVec2(origin.x, origin.y + y),
                       ImVec2(end.x, origin.y + y), gridColor);
   }
+}
+
+void ViewportPanel::handleInput(const ViewportTransform& viewport) {
+  const ImGuiIO& io = ImGui::GetIO();
+
+  if (ImGui::IsItemActivated()) {
+    selected = pick(viewport.screenToWorld(io.MousePos));
+    dragging = selected && gizmoMode == GizmoMode::Move;
   }
 
-  ImGui::SetCursorScreenPos(ImVec2(origin.x + 8.0f, origin.y + 8.0f));
-  ImGui::TextDisabled("%.0f x %.0f", size.x, size.y);
+  if (!ImGui::IsItemActive()) {
+    dragging = false;
+    return;
+  }
+
+  if (dragging && (io.MouseDelta.x != 0.f || io.MouseDelta.y != 0.f)) {
+    ImVec2 previous(io.MousePos.x - io.MouseDelta.x,
+                    io.MousePos.y - io.MouseDelta.y);
+    glm::vec2 delta =
+        viewport.screenToWorld(io.MousePos) - viewport.screenToWorld(previous);
+
+    auto& transform = selected.getComponent<sophia::TransformComponent>();
+    transform.position.x += delta.x;
+    transform.position.y += delta.y;
+  }
+}
+
+void ViewportPanel::drawSelection(const ViewportTransform& viewport) {
+  if (!selected) {
+    return;
+  }
+
+  ImDrawList* drawList = ImGui::GetWindowDrawList();
+  const auto& transform = selected.getComponent<sophia::TransformComponent>();
+
+  if (selected.hasComponent<sophia::SpriteComponent>()) {
+    glm::mat4 model =
+        selected.getComponent<sophia::SpriteComponent>().getModel(transform);
+
+    std::array<ImVec2, 4> corners;
+    for (size_t i = 0; i < UNIT_QUAD.size(); i++) {
+      corners[i] = viewport.worldToScreen(
+          glm::vec3{model * glm::vec4{UNIT_QUAD[i], 0.f, 1.f}});
+    }
+    drawList->AddQuad(corners[0], corners[1], corners[2], corners[3],
+                      SELECTION_COLOR, 2.0f);
+  }
+
+  // Mark the transform's position (the sprite's pivot), which is also all
+  // there is to show for entities without a sprite, such as the camera.
+  ImVec2 center = viewport.worldToScreen(transform.position);
+  drawList->AddCircle(center, 4.0f, SELECTION_COLOR, 0, 2.0f);
+}
+
+sophia::Entity ViewportPanel::pick(glm::vec2 world) {
+  sophia::Entity best;
+  std::optional<std::tuple<sophia::s32, float>> bestOrder;
+
+  scene.forEachEntity([&](sophia::Entity entity) {
+    if (!entity.hasComponent<sophia::SpriteComponent>()) {
+      return;
+    }
+
+    const auto& transform = entity.getComponent<sophia::TransformComponent>();
+    const auto& sprite = entity.getComponent<sophia::SpriteComponent>();
+
+    glm::mat4 model = sprite.getModel(transform);
+    // Zero size or scale; nothing to hit.
+    if (glm::determinant(model) == 0.f) {
+      return;
+    }
+
+    glm::vec4 local =
+        glm::inverse(model) * glm::vec4{world, transform.position.z, 1.f};
+    if (local.x < 0.f || local.x > 1.f || local.y < 0.f || local.y > 1.f) {
+      return;
+    }
+
+    // Same ordering the renderer draws in, so this is the one on top.
+    std::tuple order{sprite.sortOrder, transform.position.z};
+    if (!bestOrder || order >= *bestOrder) {
+      best = entity;
+      bestOrder = order;
+    }
+  });
+
+  return best;
 }

editor/panels/viewport_panel.hpp

@@ -1,27 +1,64 @@
 #pragma once
 
+#include <sophia/entity.hpp>
 #include <sophia/frame_info.hpp>
 #include <sophia/handles.hpp>
+#include <sophia/math.hpp>
+#include <sophia/scene.hpp>
 #include <sophia/ui/panel.hpp>
 #include <sophia/ui/ui.hpp>
 
+/**
+ * Shows the scene through its active camera. Click a sprite to select it,
+ * drag it to move it (in Move mode).
+ *
+ * Picking and moving are 2D: they assume an orthographic camera rotated only
+ * around Z, and work in the z = 0 plane.
+ */
 class ViewportPanel : public sophia::Panel {
  public:
-  ViewportPanel(sophia::UI& ui, sophia::RenderTargetHandle target)
+  ViewportPanel(sophia::UI& ui, sophia::RenderTargetHandle target,
+                sophia::Scene& scene, sophia::Entity& selected)
       : Panel{{.name = "Viewport",
                .windowFlags = ImGuiWindowFlags_NoScrollbar |
                               ImGuiWindowFlags_NoScrollWithMouse}},
         ui{ui},
-        target{target} {}
+        target{target},
+        scene{scene},
+        selected{selected} {}
 
   void onUpdate(const sophia::FrameInfo& frameInfo) override;
 
  private:
+  // Where the scene image is on screen this frame, and the camera looking
+  // through it.
+  struct ViewportTransform {
+    ImVec2 origin;
+    ImVec2 size;
+    glm::mat4 viewProjection;
+    glm::mat4 inverseViewProjection;
+
+    ImVec2 worldToScreen(const glm::vec3& world) const;
+    glm::vec2 screenToWorld(const ImVec2& screen) const;
+  };
+
+  void drawToolbar();
+  void drawGrid(ImVec2 origin, ImVec2 size);
+  void handleInput(const ViewportTransform& viewport);
+  void drawSelection(const ViewportTransform& viewport);
+
+  // The top-most sprite under `world`, or a null Entity.
+  sophia::Entity pick(glm::vec2 world);
+
   sophia::UI& ui;
   sophia::RenderTargetHandle target;
+  sophia::Scene& scene;
+  sophia::Entity& selected;
 
   enum class GizmoMode { Move, Rotate, Scale };
 
   GizmoMode gizmoMode = GizmoMode::Move;
   bool showGrid = true;
+  // Set while a drag that started on the selected entity is moving it.
+  bool dragging = false;
 };